Either by homopolymerization or by copolymerization with other substances, α,β-unsaturated ethers are industrially important substances for many types of synthetic resins, adhesives, lubricating oils and as intermediates for drugs, agricultural chemicals, perfumes, etc. Thermolysis of acetals is commonly known as a method for producing α,β-unsaturated ethers. In general, a catalyst is used in the thermolysis reaction.
With respect to such catalysts, patent document 1 discloses sulfates of metals having a higher ionization tendency than hydrogen, and catalysts wherein these metal sulfates are supported on a solid carrier such as alumina or silica gel. The patent document illustrates the supported catalysts by describing catalysts wherein calcium sulfate, manganese sulfate, etc. are supported on alumina, magnesium silicate, etc. Although these catalysts show relatively high catalytic performance in terms of conversion of raw materials, there are cases where the selectivity is inadequate. The document does not consider the life of the catalysts.
There are also disclosed carbonates and molybdates (for example, refer to patent document 2), and oxides or carbonates of alkali metals or alkaline earth metals (for example, refer to patent document 3). These are inadequate in terms of catalytic performances such as degree of conversion and selectivity, and are severely degraded due to coking. Furthermore, the mechanical strength of the catalysts is poor, and there are concerns over problems such as catalyst fragmentation when the catalysts are used in actual plants.
Furthermore, silica/magnesia (for example, refer to patent document 4), niobic acids (for example, refer to patent document 5), magnesium oxide (for example, refer to patent document 6), and base-treated zeolites (for example, refer to patent document 7) are also cited as examples of the reaction catalysts. However, these catalysts too have poor catalytic performances such as conversion and selectivity, and large amounts of coke are deposited to shorten the catalyst life.
A patent wherein a calcium salt of phosphoric acid is used as a catalyst to effect thermolysis of an acetal is also disclosed (for example, refer to patent document 8) In detail, calcium phosphate Ca3(PO4)2, calcium hydrogen phosphate CaH(PO4), etc. are used to catalyze thermolysis reaction of acetaldehyde diisobutyl acetal. However, these catalysts too have inadequate catalytic performances such as conversion and catalyst life.
On the other hand, a method which uses lithium phosphate (for example, refer to patent document 9) as a catalyst is disclosed. Although this catalyst shows relatively high catalytic performance in terms of selectivity and suppresses coke deposition, the degree of conversion is inadequate.
There are also disclosed a catalyst system wherein lithium phosphate is supported on silica (for example, refer to patent document 10) and a catalyst system wherein a salt of an alkali metal or alkaline earth metal is added to a mixture of lithium phosphate and silica sol (for example, refer to patent document 11). However, these catalyst systems have insufficient conversion.
Therefore, there has been a demand for reaction catalysts which simultaneously satisfy both high catalytic performance and long catalyst life, and which can efficiently and stably produce an α,β-unsaturated ether for a long time.
[Patent Document 1] Japanese Examined Patent Application Publication No. S41-5376
[Patent Document 2] Japanese Examined Patent Application Publication No. S49-45382
[Patent Document 3] Japanese Unexamined Patent Application Publication No. S57-139030
[Patent Document 4] Japanese Unexamined Patent Application Publication No. H10-175904
[Patent Document 5] Japanese Unexamined Patent Application Publication No. H09-143117
[Patent Document 6] Japanese Unexamined Patent Application Publication No. H08-277237
[Patent Document 7] Japanese Unexamined Patent Application Publication No. S62-87247
[Patent Document 8] Japanese Examined Patent Application Publication No. S54-1683
[Patent Document 9] Japanese Unexamined Patent Application Publication No. H05-229977
[Patent Document 10] Japanese Unexamined Patent Application Publication No. S58-32838
[Patent Document 11] Japanese Unexamined Patent Application Publication No. S57-185232